System for coating a stent

ABSTRACT

A systems and method for reducing coating defects on a stent may involve a support apparatus comprising wire cage for carrying a stent. The support apparatus may have no structure that extends inside the stent. A support apparatus may include a plurality of wires that pass through the stent but do not pass through the midplane of the stent. A support apparatus may contact only the proximal ends of the stent. The method may involve keeping the stent in motion during a spray coating process to prevent the stent from having a point remain in continuous contact with a support apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application No. 12/554,671, filed onSep. 4, 2009, now U.S. Pat. No. 8,573,148, which application isincorporated herein by reference.

FIELD OF THE INVENTION

Briefly and in general terms, the present invention generally relates tocoating a medical device and, more specifically, to a system and methodfor supporting a stent during a coating process.

BACKGROUND OF THE INVENTION

In percutaneous transluminal coronary angioplasty (PTCA), a ballooncatheter is inserted through a brachial or femoral artery, positionedacross a coronary artery occlusion, and inflated to compress theatherosclerotic plaque to open, by remodeling, the lumen of the coronaryartery. The balloon is then deflated and withdrawn. Problems with PTCAinclude formation of dissections, intimal flaps and torn arteriallinings, all of which can create another occlusion in the lumen of thecoronary artery. Moreover, thrombosis and restenosis may occur severalmonths after the procedure and create a need for additional angioplastyor a surgical bypass operation. Stents are used to address these issues.Stents are small, intricate, implantable medical devices and aregenerally implanted to stop negative remodeling, reduce occlusions,inhibit thrombosis and restenosis, and maintain patency within vascularlumens such as, for example, the lumen of a coronary artery.

The treatment of a diseased site or lesion with a stent involves bothdelivery and deployment of the stent. Stent delivery refers tointroducing and transporting the stent through an anatomical lumen to adesired treatment site, such as a lesion in a vessel. An anatomicallumen can be any cavity, duct, of a tubular organ such as a bloodvessel, urinary tract, and bile duct. Stent deployment corresponds toexpansion of the stent within the anatomical lumen at the regionrequiring treatment. Delivery and deployment of a stent are accomplishedby positioning the stent about one end of a catheter, inserting the endof the catheter through the skin into an anatomical lumen, advancing thecatheter in the anatomical lumen to a desired treatment location,expanding the stent at the treatment location, and removing the catheterfrom the lumen with the stent remaining at the treatment location.

In the case of a balloon expandable stent, the stent is mounted about aballoon disposed on the catheter. Mounting the stent typically involvescompressing or crimping the stent onto the balloon prior to insertion inan anatomical lumen. At the treatment site within the lumen, the stentis expanded by inflating the balloon. The balloon may then be deflatedand the catheter withdrawn from the stent and the lumen, leaving thestent at the treatment site. In the case of a self-expanding stent, thestent may be secured to the catheter via a retractable sheath. When thestent is at the treatment site, the sheath may be withdrawn which allowsthe stent to self-expand.

Stents are often modified to provide drug delivery capabilities tofurther address thrombosis and restenosis. Stents may be coated with apolymeric carrier impregnated with a drug or therapeutic substance. Aconventional method of coating includes applying a composition includinga solvent, a polymer dissolved in the solvent, and a therapeuticsubstance dispersed in the blend to the stent by immersing the stent inthe composition or by spraying the composition onto the stent. Thesolvent is allowed to evaporate, leaving on the stent strut surfaces acoating of the polymer and the therapeutic substance impregnated in thepolymer.

The size of the treatment region within an anatomical lumen may vary.Multiple stents may be deployed adjacent to each other to treatrelatively large regions of a vessel. However, positioning anddeployment of multiple stents can be time consuming and may require aspecialized delivery device capable of accommodating multiple stents.There are also issues associated with the regions where the stents meet.If the multiple stents are not abutted closely, there can be regionsbetween the stents which are not treated. To avoid this, when serialstents are implanted, they are typically overlapped. Overlapping createsother issues. The overlapped stent regions are stiffer and allow forless natural movement of the vessel. They also have a double thicknessof struts which must be endothelialized for complete healing and, in thecase of drug eluting stents, they have double the load of drug andcarrier polymer. There can be certain economies associated with using asingle 2× length stent as apposed to two 1× length stents as themanufacturing cost of producing a 2× length stent is not twice the costof producing two 1× length stents. For these many reasons, longer stentsmay be used, such as stents with an overall length greater than 30 mm.However, methods and devices for coating shorter stents may produce agreater incidence of coating defects in longer stents. Coating defectsmay include non-uniform surface characteristics, non-uniform thickness,bare spots, and flaking FIGS. 13 and 14 show coating defects on theluminal or inner surface of a stent having a 4 mm overall diameter and38 mm overall length. It is desirable to minimize coating defects forseveral reasons. Coating defects can serve as an initiation site forcoating peeling or flaking that can create embolic debris. The roughsurface generated, and stagnant regions of blood flow in the case offlaps or packets can serve as a nidus for thrombus formation.Furthermore, coating defects can lead to undue variation in the amount,concentration, and release rate of the drug from the stent coating.

Accordingly there is a continuing need for a coating method and systemthat minimizes stent coating defects, especially for longer stents.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention is directed to asystem and method for coating a stent having an outer surface facingradially outward and an inner surface facing radially inward, the innersurface forming a passageway that extends through the center of thestent from a distal end of the stent to a proximal end of the stent, thepassageway having a circular opening at each of the distal and proximalends, the stent having a central axis extending through the center ofthe circular openings.

In some aspects of the present invention, the system comprises anapparatus that supports the stent from the outer surface of the stent orfrom the distal end and the proximal end of the stent, wherein no partof the apparatus intersects a midplane of the stent, the midplanelocated halfway between the distal and proximal ends, the outer surfaceof the stent defining the outer boundary of the midplane, the midplaneperpendicular to the central axis of the stent. The system alsocomprises a coating device adjacent to the apparatus, the coating deviceconfigured to discharge a coating substance onto the stent.

In some aspects of the present invention, the method for coating a stentcomprises retaining the stent on an apparatus that supports the stentfrom the outer surface of the stent or from the distal end and theproximal end of the stent, wherein no part of the apparatus intersects amidplane of the stent, the midplane located halfway between the distaland proximal ends, the outer surface of the stent defining the outerboundary of the midplane, the midplane perpendicular to the central axisof the stent. The method also comprises discharging a coating substanceonto the stent.

In some aspects, the system comprises a cage including a wire forming aboundary of a holding space within the cage. The system also comprises amotor configured to rotate the cylindrical cage. The system furthercomprises a coating device located outside the holding space, thecoating device configured to discharge a coating substance, the coatingdevice oriented to discharge the coating substance toward the cage.

The features and advantages of the invention will be more readilyunderstood from the following detailed description which should be readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a stent showing a stacked set ofring structures forming a portion of an overall tubular structure.

FIG. 2 is a simplified view of an entire stent showing an overalltubular structure formed by a distal segment, a middle segment, proximalsegment.

FIG. 3 is a cross-sectional view along line 3-3 of FIG. 2, showinginward and outward facing surfaces of the stent.

FIG. 4 is a perspective view of a support apparatus having no structureinside the central passageway of a stent, showing the stent enclosedwithin a wire cage positioned adjacent nozzles for applying a coatingsubstance onto the stent.

FIG. 5 is a perspective view of a support apparatus having no structureinside the central passageway of a stent, showing the stent and ahelical wire that spirals around the stent.

FIG. 6 is a perspective view of a support apparatus having no structurepassing through the midplane of the stent, showing the stent retained bya plurality of wires including end wires that support the end of thestent and transverse wires that rotationally engage the stent.

FIG. 7 is a perspective view of a support apparatus having no structurecontacting a stent except at distal and proximal ends of the stent,showing the stent supported by a plurality of engaging elementsconfigured to mate with the ring structure at the distal and proximalends of the stent.

FIG. 8 is a perspective view of radially protruding elements forsupporting and/or rotating a stent.

FIG. 9 is a perspective view showing a stent rotated by a tangentialstream of air from an air nozzle.

FIG. 10 is a cross-sectional view along line 10-10 in FIG. 9.

FIG. 11 is a cross-sectional view of a stent rotated by two tangentialstreams of air from separate air nozzles.

FIG. 12 is a perspective top view of a stent rotated by a stream of aircirculated around the stent by a cylindrical surface.

FIGS. 13 and 14 are photographs of stent portions, showing coatingdefects on the inner surface of the stent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in more detail to the exemplary drawings for purposes ofillustrating embodiments of the invention, wherein like referencenumerals designate corresponding or like elements among the severalviews, there is shown in FIG. 1 a stent 10 having an overall body shapethat is hollow and tubular. FIG. 1 shows a proximal portion of the stent10. In some embodiments, the stent can be made from wires, fibers,coiled sheet, with or without gaps, or a scaffolding network of rings.The stent can have any particular geometrical configuration, such as asinusoidal or serpentine strut configuration, and should not be limitedto what is illustrated in FIG. 1. The variation in stent patterns isvirtually unlimited. The stent can be balloon expandable orself-expandable, both of which are well known in the art. The stent ispreferably for cardiovascular use. In other embodiments, the stent canbe used in another anatomical lumen, including without limitationperipheral vasculature.

FIGS. 1 and 2 show stents with two different stent patterns. The stentsare illustrated in an uncrimped or expanded state. In both FIGS. 1 and2, the stent 10 includes many interconnecting struts 12, 14 separatedfrom each other by gaps 16. The struts 12, 14 can be made of anysuitable material, such as a biocompatible metal or polymer. In FIG. 2,the stent 10 has an overall body 52 having a tube shape with a centralpassageway 17 passing through the entire longitudinal length of thestent. The central passageway has two circular openings, there being onecircular opening at each of the distal and proximal ends 22, 24 of theoverall tubular body 52. A central axis 18 runs through the centralpassageway in the center of the tubular body. At least some of thestruts 12 are arranged in series to form sinusoidal or serpentine ringstructures 20 that encircle the central axis 18. The ring structures 20are arranged serially along the central axis 18 to form the overalltubular body 52 of the stent 10. Each ring structure 20 is connected toan immediately adjacent ring structure 20 by interconnecting struts 14.One ring 20 is located at the distal end 22 of the stent 10, and anotherring 20 is located at the opposite, proximal end 24 of the stent.

FIG. 3 is an exemplary cross-sectional view of the stent 10 along line3-3 in FIG. 2. There can be any number of struts 12, 14 along line 3-3,which runs perpendicular to the central axis 18 of the stent 10. In FIG.3, the cross-section of seven struts 12, 14 are shown for ease ofillustration.

As shown in FIG. 3, the struts 12, 14 in cross-section are arranged in acircular pattern having an outer diameter 26 and an inner diameter 28.The circular pattern encircles the central axis 18. A portion of thesurface of each strut faces radially inward in a direction 30 facingtoward the central axis 18. A portion of the surface of each strut facesradially outward in a direction 32 facing away from the central axis 18.The various stent surfaces that face radially outward collectively formthe outer surface 34 of the stent 10. The various stent surfaces thatface radially inward collectively form the inner surface 36 of the stent10.

The terms “axial” and “longitudinal” are used interchangeably and relateto a direction, line or orientation that is parallel or substantiallyparallel to the central axis of a stent or a central axis of acylindrical structure. The term “circumferential” relates to thedirection along a circumference of a stent or a circular structure. Theterms “radial” and “radially” relate to a direction, line or orientationthat is perpendicular or substantially perpendicular to the central axisof a stent or a central axis of a cylindrical structure. For example, inFIG. 3, arrows 30, 32 point in opposite radial directions and the outerand inner diameters 26, 28 can be measured along radial directions.

Referring again to FIG. 2, the stent 10 has an overall length 40 that ismeasured axially from the distal end 22 to the proximal end 24, alongthe entire tubular body 52 of the stent. The stent 10 also has an axialmidpoint 42 within the central passageway 17. The axial midpoint 42 isshown through a partial cutaway of the overall tubular body of the stent10. The axial midpoint 42 is located on the central axis 18 and half-waybetween the distal and proximal ends 22, 24 of the stent 10. The axialmidpoint 42 is surrounded by the struts 12, 14 and may be encircled byone of the ring structures 20. A radial midline 44 intersects thecentral axis 18 at the axial midpoint 42.

A midplane 45 runs through and contains the axial midpoint 42 and theradial midline 44. The midplane 45 is bounded by the outer surface 34 ofthe stent and is located half way between the distal and proximal ends22, 24 of the stent 10. That is, the midplane 45 does not extend beyondthe outer surface 34 of the stent 10. The outer surface 34 defines, orat least forms part of, the outer boundary of the midplane 45. Themidline 44 and midplane 45 are perpendicular to the central axis 18.

The stent 10 also has a distal segment 46, a middle segment 48, and aproximal segment 50. The distal segment 46 starts at the distal end 22and extends toward the proximal end 24. The proximal segment 50 startsat the proximal end 24 and extends toward the distal end 22. The middlesegment 48 contains the axial midpoint 42 and is located between thedistal and proximal segments 46, 50. Together the distal, middle, andproximal segments 46, 48, 50 form the overall tubular body of the stent10.

Referring again FIGS. 1 and 2, the struts 12 of each ring structure 20are arranged end to end, forming a sinusoidal or undulating pattern. Inthe illustrated embodiments, the undulating pattern of each ringstructure 20 includes a series of V- or W-like shapes arrangedcircumferentially. The ends of the struts 12 are connected by bendingelements 54 (FIG. 1) which are configured to bend and flex duringcrimping, stent delivery, and stent deployment. The bending elements 54allow elongate portions of the struts 12, which are relatively straight,to move in relation to each other, thereby allowing the elongateportions to collapse toward one another during crimping and to spreadapart during stent deployment.

As shown in FIG. 1, the undulating pattern of each ring structure 20includes an alternating series of peaks 56 and valleys 58 at the bendingelements 54 (elements 56, 58 and 54 are not in FIG. 2, but are inFIG. 1. Should this first sentence refer to FIG. 1?). The peaks 56 andthe valleys 58 are high points and low points, respectively, on eachring structure 20. At the distal and proximal ends 22, 24 of the stent10, crowns 60 protrude out in axial directions and form thecircumferential edges of the overall tubular body 52 of the stent 10.The crowns can be either peaks 56 or valleys 58. The crowns 60 at theproximal end 24 (FIG. 2) form the proximal edge of the stent 10. Thecrowns 60 at the distal end 22 (FIGS. 1 and 2) form the distal edge ofthe stent 10. The crowns 60 are spaced apart from each other bycircumferential gaps 62 bounded in part by elongate portions of thestruts 12 and bending elements 54.

FIG. 4 shows a stent 70 with a slight curvature over its overall length.The stent 70 can be over 30 mm in overall length. The curvature may bean intentional aspect of the stent design or may be the result of amanufacturing variation. Manufacturing variations that may causecurvature could include handling of the stent during secondaryprocesses, such as descaling and electropolishing of metal stent struts,weighing processes, or manipulation of the stent between the variousmanufacturing steps. The stent central axis 71 is a straight line thatpasses through the respective center point of each circular opening ofthe stent central passageway at the distal and proximal ends of thestent.

The stent 70 is placed in and enclosed within a small cylindrical cage72. The stent 70 will move about or rattle within the cage 72 as thecage is rotated about its longitudinal axis 73. The stent 70 may moveabout due to rotation of the cage and/or under the action of a sprayplume 74 of coating substance projected out of one or more nozzles 76located at a distance away from the cage, or from the action of gasdirected from a drying nozzle. The nozzles 76 are configured todischarge a coating substance using any device including but not limitedto an air pressure source, an external air assisted atomizer, aninternal air assisted atomizer, a piezoelectric transducer, and anelectrostatic device.

In some embodiments, the cage is not rotated and the stent moves aboutsolely due to the spray plume 74 which applies a rotational force on thestent 70. The nozzles 76 may be moved relative to the cage so as tocause a change in direction of the force applied by the spray plume onthe stent 70 that keeps the stent constantly moving. Also, the cage canbe moved relative to the nozzle so as to cause a change in direction ofthe force applied by the spray plume on the stent 70 that keeps thestent constantly moving. The relative movement can be rotational,linear, or a combination of both.

The stent 70 is supported by the cage 72, so there can be one or morecontact points between the stent and cage at any time. Movement of thestent 70 within the cage 72, whether due to cage rotation, the sprayplume or other cause, assures that there are no permanent contact pointsbetween the cage and stent. That is, a particular point of contactbetween the stent 70 and the cage 72 exists only momentarily before thestent shifts in relation to the cage and forms a different point ofcontact. The periodic or continuous movement of the stent allows allportions of the stent to be coated over a period of time. Also, itbelieved that constant movement reduces or prevents the occurrence ofcoating defects due to pooling or webbing of the coating substance atcontact points. The inner diameter of the cage is sized large enough sothat stents with a maximum degree of bend can still rattle around insidethe cage by at least a small amount.

With continued reference to FIG. 4, at the distal end 74 of the cage 72there is a removable cap 76. Removal of the cap 76 from the cage 72allows a stent to be placed inside and removed from the cage 72. At theproximal end 78 of the cage 72 there is a connection member 80 that maybe engaged to an electric motor or other machine that rotates orlinearly translates the cage 72.

The cage 72 includes circumferential wires 82 and longitudinal wires 84that support and retain the stent 70. Any wire pattern may be used. Theillustrated embodiment includes five circumferential wires 82 and fourlongitudinal wires 84, although any number of wires 82, 84 may be usedas appropriate for the size of the stent 70. In some embodiments, thecircumferential wires 82 are inside the longitudinal wires 84 tominimize the size of the temporary contact points between the stent 70and the cage 72.

The cage wires 82, 84 form, at least in part, the boundary of a holdingspace for holding the stent 70. In some embodiments, the number of cagewires 82, 84 are minimized so that there is just enough to support andretain the stent 70. The number of wires may depend on the size andshape of the stent. For example, there can be only one longitudinal wire84 with two or more circumferential wires 82. In a further example,there can be only three longitudinal wires 84 with no circumferentialwires. Minimizing the number of cage wires will also minimize shadowingor masking of the stent 70 by the wires. Shadowing and masking refers tothe condition where one or more of the cage wires covers a portion ofthe stent 70 so that the portion receives less coating substance thanother portions of the stent. Inducing the stent 70 to continuously moveor rattle inside the cage 72 during all or part of the coating processwill also allow portions of the stent that were masked by the cage wiresto be adequately coated at a later time during the coating process. Anydiminishment of the spray flux by the cage wires is expected to beaveraged out due to movement of the stent 70 relative to the cage 72and/or nozzles 76.

In some embodiments, contact points between the stent 70 and one or moreof the cage wires 82, 84 lasts no longer than the time for rotating thecage by a predetermined angle of rotation about the cage longitudinalaxis 73. The predetermined angle of rotation can be 720 degrees (tworevolutions), more narrowly 360 degrees (one revolution), and morenarrowly 180 degrees (half a revolution), and more narrowly 90 degrees(quarter revolution). In some embodiments, the cage wires are configuredso that they have no point that remains in continuous contact with thestent 70 while the cage axially rotates 720 degrees, more narrowly 360degrees, and more narrowly 180 degrees, and more narrowly 90 degrees.

In some embodiments, the cage 72 is a substantially open structure, inthat the cage allows the spray plume to enter the cage and allows anysprayed substance that does not contact the stent to pass through theother side of the cage with minimal obstruction. In this manner,accumulation of the coating substance inside the cage is minimized orprevented altogether.

In some embodiments, the stent 70 is forced to rotate about the stentcentral axis 71. In some embodiments, the cage 72 prevents the stent 70from rotating on an axis perpendicular to the stent central axis 71during the spray coating process. In some embodiments, the cage 72 keepsthe stent oriented so that the stent central axis 71 remains parallel orsubstantially parallel to the cage longitudinal axis 73. In someembodiments, the cage 72 is sized to allow only one stent to fit insidethe cage. In some embodiments, the cage 72 is sized to prevent the stent70 from moving out from the path of the spray plume 74. That is, thecage elements 82, 84 prevent the stent 70 from being forced from thespray area directly in front of the nozzles 76. In some embodiments, thenozzles 76 are oriented tangentially to the outer surface of the stent.

It will be appreciated that the cage of FIG. 4 includes no part thatextends into the central passageway of the stent 70. Also, all points ofcontact between the sent 70 and the cage 72 are only on the stent outersurface. The cage wires can be made of any material, including but notlimited to metal, polymer, natural fiber, or combinations thereof. Thecage wires can be a flexible string, fiber or filament that is pulled intension.

FIG. 5 shows a cage 86 with elements similar to the cage 72 of FIG. 4except that the cage 86 includes a helical wire 85 that spirals aroundthe stent 70. The helical wire 85 defines, at least in part, a holdingspace in which the stent 70 is located. The helical wire 85 defines, atleast in part, the boundary of the holding space. As the cage 86 isrotated, portions of the helical wire 85 that were masking the stent 70from the spray plume 74 will move out of the way to allow the stent tobe coated more uniformly. It is also believed that rotation of thehelical wire about the cage central axis 73 will keep points of contactbetween the stent and the cage continuously changing. In someembodiments, the cage 86 includes multiple coiled wires forming theboundary of a holding space for the stent. In some embodiments, the cage86 has no longitudinal wires that form a boundary for the holding space.

Referring next to FIG. 6, the ends of a stent 90 are supported on thinwires 92, 98 of a support apparatus 88. A middle segment of the stent 90is rotated by other wires 94, 96. The wires 92, 94, 96, 98 extend asmall distance into the stent central passageway, though none of thewires pass through the stent midplane 91. Longitudinal end wires 92, 98extend partially into the proximal end 100 and distal end 102 of thestent. The end wires 92, 98 enter the stent central passageway throughthe circular openings formed by ring structures at the proximal anddistal ends 100, 102, as opposed to entering through gaps between stentstruts. The end wires 92, 98 are located only at the end segments of thestent tubular body and do not pass through the middle segment of thestent tubular body. In some embodiments, the end wires 92, 98 extendinto the stent tubular body by no more than 40% of the overall length ofthe stent, more narrowly no more than 25% of the overall length of thestent, more narrowly no more than 10% of the overall length, and morenarrowly no more than 5% of the overall length.

The end wires 92, 98 are parallel or substantially parallel to thecentral axis 93 of the stent 90. The end wires 92, 98 do not transmitany significant rotational torque to the stent 90. The end wires 92, 98by themselves are incapable of rotating the stent 90 about the stentcentral axis 93. The end wires 92, 98 may be journaled or coupled to thesupport apparatus 88 in such a way to allow the end wires 92, 98 toaxially rotate or spin freely and independently of other parts of thesupport apparatus. In another embodiment, the end wires 92, 98 onlyrotate if the support apparatus 88 is rotated.

The end wires 92, 98 are held in position by support members 104 thatrun the entire overall length of the stent 90. A release device 106attached to one of the end wires 98 is configured to allow the end wireto be retracted or slid out of the stent 90 so as to allow removal ofthe stent and installation of another stent. The release device 106 mayinclude a knob for user manipulation and a spring that biases or urgesthe end wire 98 into the stent.

Transverse wires 94, 96 transmit torque or rotational force to the stent90. The illustrated embodiment shows two transverse wires 94, 96, thoughany number of transverse wires 94, 96 may be used to rotate the stent90. The transverse wires 94, 96 pass through gaps between stent struts.The transverse wires 94, 96 extend at a ninety-degree angle or othernon-zero angle relative to the central axis of the stent 90. Thetransverse wires 94, 96 are connected to a connection member 108 at asecond end of the support apparatus 88. The connection member 108 isconfigured to transmit torque or rotational force from an electric motorto the transverse wires 94, 96. Activating the motor causes axialrotation of the connection member 108, which causes rotation of thetransverse wires 94, 96, which cause rotation of the stent 90. In someembodiments, the transverse wires 94, 96 may connect to support members104.

The transverse wires 94, 96 may be sufficiently flexible to allow a userto pull the tips of the wires 94, 96 out of the stent 90 to allowremoval of the stent and installation of another stent. In someembodiments, the transverse wires 94, 96 enter a segment of the overallstent body that does not contain the end wires 92, 98.

As the stent 90 with the support apparatus 88, the stent will shiftaround slightly and, thus, avoid any permanent contact points betweenthe stent and the support wires 92, 94, 96, 98. That is, contact pointsbetween the stent 70 and the support apparatus 88 exist temporarilyduring the coating process. In some embodiments, contact points betweenthe stent and one or more of the wires 92, 94, 96, 98 lasts no longerthan the time for rotating the stent by a predetermined rotational angleabout the stent central axis. The predetermined angle can be 720degrees, more narrowly 360 degrees, and more narrowly 180 degrees. Insome embodiments, the wires 92, 94, 96, 98 are arranged and configuredso that they have no point that remains in continuous contact with thestent 90 while the stent rotates 720 degrees about the stent centralaxis, more narrowly 360 degrees, and more narrowly 180 degrees.

With continued reference to FIG. 6, in some embodiments the stent 90 maybe rotated under the action of a spray plumes 74 of coating substanceprojected out of one or more spray nozzles 76 located at a distance awayfrom the support apparatus 88. In some embodiments, there are notransverse wires and the stent 90 is allowed to rotate freely andindependently of the support apparatus 88. In some embodiments, stent 90is induced to move solely due to the spray plume 74 applying arotational force on the stent. The nozzles 76 may be oriented so as todirect the spray plume 74 tangentially to the stent outer surface. Thenozzles 76 and the support apparatus 88 may be moved relative to eachother so as to cause a change in direction of the force applied by thespray plume on the stent 90 that keeps the stent constantly moving.

Referring next to FIG. 7, a support apparatus 120 includes two supportdevices 122, 124 at opposite ends of a stent 126. The support devices122, 124 are connected to each other by a base member 127 that spanslongitudinally across the entire overall length of the stent. Thesupport devices 122, 124 include protruding elements 128 that projectradially outward away from each other. The protruding elements 128 aresized and shaped to interdigitate with the ring structures at theproximal and distal ends of the stent.

In some embodiments, the protruding elements 128 are shaped to mate withthe undulating ring structures at the proximal and distal ends. Theprotruding elements 128 fit into the circumferential gaps separating thecrowns of the ring structures at the proximal and distal ends. Theprotruding elements 128 extend partially into the stent centralpassageway. When the support devices 122, 124 are rotated, theprotruding elements 128 exert torque or a rotational force on elongateportions of the stent struts forming the ring structures. When rotated,the protruding elements 128 push the stent struts in a circumferentialdirection.

In some embodiments, the support devices 122, 124 include a biasingdevice, such as a spring or an electric motor, that biases or urges theprotruding elements 128 into the circumferential gaps. The biasingdevices may also allow the support devices 122, 124 to slide and moveapart from each other to allow removal of the stent 126 and installationof another stent on the support apparatus 120. In a further embodiment,one or both of support devices 122, 124 are slidable with respect to oneanother to accommodate stents of varying length.

The support devices 122, 124 can include any number of protrudingelements 128. For example, each support device 122, 124 can have onlyone protruding element 128 or only two protruding elements. In someembodiments, the protruding elements 128 push axially against bendingelements that interconnect the stent struts. In some embodiments, theprotruding elements 128 are arranged and positioned so as to support thestent 126 loosely, wherein the protruding elements do not press axiallyagainst the bending elements or any other part of the stent. In thismanner, the stent 126 may shift position on the support devices 122, 124so that there is no point on the support devices 122, 124 that remainsin continuous contact with the stent 90 while the stent rotates 720degrees about the stent central axis, more narrowly 360 degrees, andmore narrowly 180 degrees, and more narrowly 90 degrees.

In some embodiments, one of the support devices 124, is journaled orrotatably coupled on a bearing 130 of the support apparatus 120 in sucha way to allow the support device 124 to axially rotate or spin freelyand independently of other parts of the support apparatus. In this way,the support device 124 is rendered incapable of applying any torque orrotational force on the stent 126.

In some embodiments, one of the support devices 122 is supported on abearing 132 and is actively driven by an electric motor or machineengaged on a connection member 134 passing through the bearing 132. Insome embodiments, the opposite support device 124 is not activelydriven, but is allowed to rotate freely due to rotation of the stent126.

The base member 127 is positioned opposite a coating applicator 136configured to project a coating substance toward the stent 126. Thestent 126 is located between the coating applicator 136 and the basemember 127 to avoid shadowing and masking of the stent 126. The coatingapplicator 136 may be a spray nozzle or series of spray nozzles.

With continued reference to FIG. 7, in some embodiments the stent 126may be rotated under the action of a spray plume 138 from the coatingapplicator 136. In some embodiments, the support devices 122, 124 do notinduce rotation of the stent 126 so that the stent is allowed to rotatefreely and independently of the support apparatus 120. In someembodiments, the stent 126 is induced to move solely due to the sprayplume 138 applying a rotational force on the stent. In some embodiments,the coating applicator 136 is oriented so that the spray plume 138 isconcentrated on an off-center or tangential portion of the stent toinduce axial rotation of the stent.

It will be appreciated that in FIG. 7 no portion of the supportapparatus 120 contacts the stent 126 except at end segments of thestent. In some embodiments, no portion of the support apparatus 120contacts the stent 126 except at the outermost ring structures at thedistal and proximal ends of the stent. In some embodiments, there are nopoints on the stent 126 that continuously remain in contact with thesupport apparatus 120 while the stent rotates.

In some embodiments, as shown in FIG. 8, the support devices 122, 124include a tapered longitudinal element 140. The protruding elements 128project radially outward from the longitudinal element 140 and an axisof rotation 141 of the support device. The longitudinal element 140 isshaped and configured to enter the central passageway of the stentthrough the circular openings formed by ring structures at the proximaland distal ends of the stent, as opposed to entering through gapsbetween stent struts. In some embodiments, the longitudinal element 140extends into the stent tubular body up to 40% of the overall length ofthe stent, more narrowly up to 25% of the overall length of the stent,more narrowly up to 10% of the overall length, and more narrowly up to5% of the overall length. In some embodiments, the longitudinal element140 is a thin wire. In some embodiments, no part of the support devices122, 124 extend into the central passageway of the stent beyond theoutermost ring structures at the proximal and distal ends of the stent.

Referring now to FIGS. 9 and 10, rotation of a stent 150 can be inducedby a focal air flow at a lower or upper edge of the stent. The stent 150may be supported in any manner that allows axial rotation of the stent,including but not limited to the support structures described inconnection with FIGS. 4-8. An air nozzle 152 is configured andpositioned to project a focused stream of air in a direction 154 that issubstantially tangential to the abluminal or outer surface 156 of thestent 150. The air nozzle 152 is connected to a pressurized air source.All or a majority of the air from the air nozzle 154 is directed belowthe central axis 158 of the stent 150 so that the stent is induced torotate about the central axis as indicated by arrow 160. In otherembodiments, the air from the air nozzle 154 is concentrated above thecentral axis 158 or on any one side of the central axis. In someembodiments, the air nozzle 152 is connected to a source providing acoating substance so that the air stream includes the coating substanceto be applied on the stent 150. In some embodiments, in addition to theair nozzle 152 which provides for the rotation of stent 150, there is anadditional spray nozzle to apply the coating.

In some embodiments, as shown in FIG. 11, multiple air nozzles 152 a,152 b project separate streams of air tangentially on the stent 150. Thetangential air streams can be directed at different directions 154 a,154 b to different portions of the stent that are off-center from thecentral axis of the stent.

FIG. 12 shows a top perspective view of a stent 160 at least partiallysurrounded by a curved, cylindrical surface 162. The cylindrical surface162 extends longitudinally along the entire overall length of the stent160. The cylindrical surface 162 forms a space into which a stream ofair 164 is directed. The surface 162 is shaped to channel or direct thestream of air 164 in a circular direction 166 around the outer surfaceof the stent 160 so that the stent is induced to axially rotate aboutthe stent central axis 168 in the same circular direction 166. Thecylindrical surface 162 may have a longitudinal inlet slot opening 170into which the stream of air is directed. The cylindrical surface 162may also have a longitudinal outlet opening 172 out of which air mayescape after having been circulated around the outer surface of thestent 160.

In operation, the air stream 164 circulates around the stent 160, whichkeeps the stent constantly moving relative to the surrounding surface162 while the stent is coated with a coating substance. While the stentmoves or rattles, no part of the stent remains in continuous contactwith a support structure. The air stream 164 may include a coatingsubstance that coats the stent 160. In some embodiments a coatingsubstance is applied to the stent 160 separately from the air stream164.

In FIG. 12, the stent 160 may be supported in any manner that allowsaxial rotation of the stent, including but not limited to the supportstructures described in connection with FIGS. 4-8. In some embodiments,the stent is supported and retained solely by the cylindrical surface162. In some embodiments, the cylindrical surface 162 keeps the stent160 oriented so that the stent central axis 168 remains parallel orsubstantially parallel to the central axis 174 of the cylindricalsurface 162. In some embodiments, the cylindrical surface 162 has aplurality a circular cross-sections, the surface central axis 174 passesthrough the center point of each of the circular cross-section, and thestent central axis 168 and the surface central axis 174 are parallel orsubstantially parallel to each other. In some embodiments, thecylindrical surface 162 includes a plurality of straight lines 176 thatare parallel or substantially parallel to each other and to the stentcentral axis 168. In some embodiments, the cylindrical surface 162 issized to prevent the stent 160 from moving out from the path of the airstream 164.

In the above described embodiments, the stent can be sized for anyanatomical lumen. In some embodiments, the stent has an outer diameterof 3 mm. In some embodiments the stent is 33 mm in overall length. Inother embodiments, the stent is 38 mm in overall length. In someembodiments, the stent is over 38 mm in overall length.

In the above embodiments, the coating substance may include a polymericcarrier impregnated with a drug or therapeutic substance. The polymericcarrier may be a polymer dissolved in a solvent, and the drug dispersedin the blend. Examples of drugs that can be coated on stents using themethod of the present invention include any moiety capable ofcontributing to a therapeutic effect, a prophylactic effect, both atherapeutic and prophylactic effect, or other biologically active effectin a mammal. An agent can also be coated which has a diagnosticproperty. The drug or bioactive agents include, but are not limited to,small molecules, nucleotides, oligonucleotides, polynucleotides, aminoacids, oligopeptides, polypeptides, and proteins. In one example, thedrug or bioactive agent inhibits the activity of vascular smooth musclecells. In another example, the drug or bioactive agent controlsmigration or proliferation of smooth muscle cells to prevent or inhibitrestenosis.

Bioactive agents include, but are not limited to, antiproliferatives,antineoplastics, antimitotics, anti-inflammatories, antiplatelets,anticoagulants, antifibrins, antithrombins, antibiotics, antiallergics,antioxidants, and any prodrugs, metabolites, analogs, homologues,congeners, derivatives, salts and combinations thereof.

While several particular forms of the invention have been illustratedand described, it will also be apparent that various modifications canbe made without departing from the scope of the invention. It is alsocontemplated that various combinations or subcombinations of thespecific features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the invention. For example one end of a stent can be supportedby one end wire shown in FIG. 6 while the opposite end of the stent canbe supported with the protruding elements shown in FIG. 8. Accordingly,it is not intended that the invention be limited, except as by theappended claims.

What is claimed is:
 1. A system for coating a stent having an outersurface facing radially outward and an inner surface facing radiallyinward, the inner surface forming a passageway that extends through thecenter of the stent from a distal end of the stent to a proximal end ofthe stent, the passageway having a circular opening at each of thedistal and proximal ends, the stent having a central axis extendingthrough the center of the circular openings, the system comprising: anapparatus that supports the stent, wherein no part of the apparatusintersects a midplane of the stent, the midplane located halfway betweenthe distal and proximal ends, the outer surface of the stent definingthe outer boundary of the midplane, the midplane perpendicular to thecentral axis of the stent, and coating substance device adjacent to theapparatus, the coating device configured to discharge a coatingsubstance onto the stent, wherein the apparatus rotates the stent atleast 360 degrees about the central axis of the stent, the apparatusextends into the passageway of the stent, and the apparatus has no pointthat remains in continuous contact with the stent while the stentrotates 360 degrees about the central axis of the stent, wherein theapparatus has a point of contact that makes momentary contact with thestent while the stent rotates 360 degrees about the central axis of thestent.